In the field of material handling, flexibility is a key factor. Material handling vehicles receive, transport and place loads in a variety of applications. The loads are usually placed in tubs, pallets, containers, or the like for transportation. The vehicle is typically equipped with a pair of forks for disposal into a load opening.
The width of the load opening varies greatly depending on the type and size of the load and the application. The distance between the forks is restricted by the smallest width of the load opening of any load in the system. A vehicle in which the distance between the forks is variable is therefore desirable. A forklift truck for example, typically has forks which are hung on a carrier. That is, the forks are connected to a lift mast assembly such that they can be manually positioned depending on the width of the load opening. In U.S. Pat. No. 4,458,786 and U.S. Pat. No. 4,502,568 both issued to Charles J. P. Lebre, dated July 10, 1984 and Mar. 5, 1985, respectively, a forklift truck having a handle to vary the spacing of the forks is disclosed. However, this is a manual operation and furthermore, the forks must be moved simultaneously and the same distance.
Forklift trucks are also known to be equipped with fork spreaders. This apparatus allows the forks to be hydraulically or electrically controlled by an operator. In U.S Pat. No. 2,886,197 issued to D. A. Harris, dated May 12, 1959 a lift truck outfitted with a load clamp includes a hydraulic valve and hydraulic cylinders for moving the arms of the clamp thereby opening and closing the clamp. There is however no means for determining the exact position of the arms of the clamp other than by estimation by the vehicle operator. It is therefore difficult to position the forks the correct distance apart.
Automatic guided vehicles of the driverless type (AGV) may also be equipped with a lift mast assembly and forks. Increased flexibility is a characteristic keenly felt in these vehicles. AGV's are used to transport a great variety of loads and must therefore be able to adapt to a variety of loads and load openings. By limiting the fork width such that it is able to fit in the smallest load opening creates a problem. This makes the handling of wider loads, which typically are heavier, quite unstable. Since it is highly undesirable to add a manual operation to this otherwise operatorless vehicle, the need for a system for automatically sensing the position of each fork at any point during operation and for automatically positioning each fork relative to the load is even more critical.
The subject invention is directed at overcoming one or more of the problems as set forth above.